The app shows your scheduled arrival time and then an estimated arrival time. It changes to actual arrival once blocked. If I had to guess, it was showing your plane as "landed" and an estimated arrival time "10 minutes ago" (at the time), because they didn't update the estimate again while sitting on the tarmac waiting for the gate.

That happens a lot in those situations, where the "estimated time of arrival" has already come and gone. Once you land those times have to be updated manually, and it'd be purely a guess on their part how long exactly it'll take for the gate to open up. Seems it updated to the correct arrival on the app after your plane blocked at the gate, because what it shows is after the time of your original post.

You might see incorrect departure times every once in awhile, if the pilots kick the brakes a little early. But I don't know if I've ever seen an incorrect arrival time.