Crazy eights use of 8 to keep suit
There isn't a definitive set of rules. It's a game learned through word of mouth over generations. And house rules are easily added. All this means that not everyone plays by the same rules. Ultimately, the answer comes down to whatever rules the group agreed to use.
What? You didn't agree to a set of rules? ;) Well, the Wikipedia page for Crazy Eights has no variant listed concerning the functioning of eights. It only lists the following rule:

They can also play any 8 at any time, which allows them to declare the suit that the next player is to play; that player must then follow the named suit or play another 8.

And this version of the rules says:

An Eight may be played on any card, and the player of the Eight must nominate a suit.

In both cases, no limit is mentioned concerning the stated suit. Words such as &quot;other&quot; and &quot;change&quot; that would imply a different suit should be picked are conspicuously absent. This means the suit already being played is a valid choice.
This is consistent with how I played.