AITHA for buying concert tickets for step kids on bio mom's day?

I have been traveling for work and super busy so I haven't spend much time on the internet lately. Today I got an email about a presale had started for a concert that will take place in September of 2025, that I KNOW my kids and step kids would love to go. So I immediately jumped on and grab tickets for everyone to go as a Christmas gift. Thank goodness as tickets were going fast and thinning. After I bought the tickets, I checked the calendar and noticed it is not one of DH's days, no problem I thought, its 11 months away, just have him text ex wife. The response we got was over the top anger as "she planned to take them". So I have to ask, am I the asshole? I thought I was being super nice but here I am now at the top of the enemy list.