Your proxy bid wasn't showing at the full $25 of your maximum. It would have been at $24.50 or less.
Therefore, competing bidders could bid 50 cents or higher than the amount shown.
The bidder picked $25.01, which trumps your $25 maximum.
If there was still time left, then you, or anyone, could bid $25.51 or higher.

That's why a lot of bidders pick an odd amount to bid, rather than an even-dollar amount.