I get where you're coming from, but I honestly assume no malice. It's fairly common knowledge in tabletop circles that spindown dice will have an unbalanced distribution. They're definitely made to be used only as a counter.

Now, whether it matters if you use a weighted die to determine who goes first is a different story. If you're both using the same die, who cares?

If the opponent picked from the same pool that sounds OK.

At least way better than spindown dice, which are known to be weighted.