Oh he made plenty of mistakes, and there is plenty of room for refinement in his move choices.
-use of 66K - 66K can be punished by Natsu (-10) and it's just a bad habit to be throwing it out like that
-use of 2B on standing - 3K is better here, since it'll track step pretty well too. BB will get CH'd by 22A in this matchup, so 2B is a decent replacement, but only outside 3K range. The +2 on hit makes it pretty bad.
-should be using 6B to stop Natsu 66K on-hit followups, at -4 the i13 mid will beat her AA as well as beat the TC and TJ properties. Punish with 6K or CE, not 3B
-random CEs that didn't work
-too linear, needs to stop Natsu's 22A
-treats DGF B like adv on block
-not using iMCF setups or stopping pressure with it
-not using any BEs
-not attempting any ringouts using iMCF, 3A CH-confirms, or even 66A BE hail-marys on a ringout stage
-not hop-kicking any UB bombs
-not JGing or GIing the predictable attacks at advantage despite having plenty of meter to blow on GIs
-not GI-CEing
A lot of those problems can be fixed by using more 3A and CH confirming it into the BE. His meter use was all wrong, but I don't blame him. Yoshi's meter management is like the hardest out of any character.
That Natsu's pretty good though. It's kAb, if I'm not mistaken? I went 25-24 against that guy last we played.