Yeah, that move is perfectly okay and it is a correct way to play a side. In theory it could be exploited I suppose but it is very difficult most of the time. If I was Green in this situation playing against you, I would have shared the side with you at some point and played b5 just as Toptal did on move #19. Also, when you played f3 for move #9, now you are potentially inviting Green to play e3 which they played on #11, which will give you the opportunity to play e2, which you played on #16.
So... you played everything correctly. Playing these center 2 hexes in the middle are tricky because you have to make sure you are either getting a Closed 2 or you have to the opportunity to balance out your edge or be willing to share the side. Both you and Daniel play the sides remarkably well, especially considering how little I explained to the 2 of you compared to how much I explained to my brother, and both of you guys are still better than my brother.
Also... one more thing... I'm sure you already know this but... when sharing sides of this sort like on the Southern side of this game after Green has played #19, now there is a potential Wedge spot at c4 for BOTH players. Now both players can sacrifice a corner and Wedge so... you just have to be careful of that OR you can use it to your advantage.
Feel free to keep asking questions of this sort.

Here's a link to the game after move #19 for reference.
So... you played everything correctly. Playing these center 2 hexes in the middle are tricky because you have to make sure you are either getting a Closed 2 or you have to the opportunity to balance out your edge or be willing to share the side. Both you and Daniel play the sides remarkably well, especially considering how little I explained to the 2 of you compared to how much I explained to my brother, and both of you guys are still better than my brother.
Also... one more thing... I'm sure you already know this but... when sharing sides of this sort like on the Southern side of this game after Green has played #19, now there is a potential Wedge spot at c4 for BOTH players. Now both players can sacrifice a corner and Wedge so... you just have to be careful of that OR you can use it to your advantage.
Feel free to keep asking questions of this sort.

Here's a link to the game after move #19 for reference.