I'm a firm believer of "live, and let live".
But I'm also a believer in "keep your f*3&(&# head down".
And I'm a firm believer in "you reap what you sow".
I think what's happening here is a solid lesson in it all. There's some crazy people out there who would love nothing better to do than tear down another human being. Some people need to be torn down and they aren't -- the world isn't fair in that way, which is why I invest in real estate in the first place. I'll do my best to make my own luck, so to speak. But I also don't want to be too communicative about it -- If you bullhorn a "look at me" post, it's going to attract some attention, both positive and negative. I personally like congratulating people on their personal successes, but I guess there are wackos out there who think differently.
I, personally, don't believe the post or this individual got you fired. I bet both of those were building blocks to the end. You said it yourself..."My employer never liked me doing RE deals as it was. Whether a tenant would drop by their rent check or he knew I was flipping a house, he wanted me to be 100% owned by him." Well, lets look at what is probable from that statement -- you spent time at your W2 likely talking about hobbies/interests not related to your W2. And then you were conducting business for your non-W2 at your W2. That alone would most certainly get most of us here dropped like a bad habit, or at least reprimanded.
Its entirely possible, Todd, that your manager is just a jealous, petty person. There's plenty of those out there. But I've got to be honest, if I ran a business and paid you to be an employee, and you were conducting your own business during business hours at my place of business, right in front of the manager...I mean...put yourself in his shoes for a minute. I'm paying you to do a job for me, and you're spending time doing something else. Maybe this only happened once, but once is enough to cast doubt for most managers. I don't agree you should have been fired, but I'm also not the owner of that business in what I assume is an at-will employment state. If you run your own business in an at-will employment state, then its up to you to decide how to conduct your business.
I'm also a bit taken aback, respectfully of course, that you commented about the pandemic and how it "caught you off guard". In the same breath, this pandemic which you see as a "challenge to happenings in your professional career", became a "tenants live free" mantra. Nope. Sorry. Not buying it, dude. Goes back to the world not being fair -- you lost your job in a pandemic and so have others. For you to approach it as a personal struggle for you, and a "taking advantage and living free" opportunity for a tenant...no. We're all in this boat together. Sounds a bit selfish on your part, frankly. You're not the only dude struggling. Food for thought.
I think one of the more interesting lessons I've learned in my career is that while its entirely possible external forces impact you negatively, you should be the owner (and ultimately, the responsible party) for what happens to you. You are the ONLY person watching your six. That's a fact, especially in our professional lives. You could be better, faster, stronger, smarter than your manager ($20 says you are, no doubt) and yet, you're the one with the short end of the stick in this particular situation.
You seem like a smart, ambitious guy, and I'm glad you found another job and were hopefully not seriously impacted. Chances are you'll look back on this moment as a blessing in disguise, as others have indicated, where your manager did you a favor cutting you loose. But common sense would dictate you shouldn't have tenants coming by the job to pay you rent, you shouldn't be performing RE work while you're at your W2 (or at least hide it better...use your personal phone/tablet and don't connect to company servers), and always check who you talk non-shop with.
Good luck on your new job...coming right up on the 5th!