I must admit that I can guess why the two judges gave him round 3.
That first take down was more like a stumble in the end than a clean one and when you were on top of him you couldn't capitalise, but spend quite some time in his choke attempt. After he reversed top-bottom position he was working constantly out of your guard. When in stand-up again, you seem quite out of gas (I don't know how much that impression adds to the opinion in the judges minds) and it looks like he gets you with a decent punch. Your take down afterwards is classy and should have scored for you quite a bit, but unfortunately you just land in his guillotine attempt, which you luckily escape very quick and your positioning is good, but again you're not really able to capitalise.
So overall I think it is a close round and could have gone either way. In that way the split decision is ok and reflects the fight. If it weren't a 10-9 scoring but a 10-1 scoring, that fight would have been yours though withough doubt as round 1 was not close to decide, but clearly dominated by you.
You possibly could have ended the fight in round 1 already. Your opponent was begging not only once to be straight armbarred while you were in the mount.
My advise also, keep your hands higher, both of them. You were lucky twice when he touched you with his kicks to your head that they didn't land properly. Yes, it's easily said to keep the hands high, but hard to implement if someone has already the habbit of having them low, because they don't "feel" low. So as a tip, have yourself filmed as often as possible in training/sparring to help yourself really mentally comprehend where you have your hands so you can adjust. You may try to get the habbit of regularly pinch your cheeks between thumb and index to keep your hand position in mind.
Generally, I think you should pay more attention to protect your head. At least I had the impression that on your take down rush ins you were a bit vulnerable to possible knee kicks and you ended up in guillotine attemps several times.
But overall it was a good performance, more versatile than some of the "known names".