[codingdave]

Tell them what you just told us - you continued your search, and while interested, need to finish your ongoing interview processes before making a decision. Any organisations that cannot accept that isn't one you want to work for anyway. Likewise, if there is a problem communicating transparently with your future boss, they aren't someone you want to work for.

The only thing from your post that I wouldn't say is "wait a few weeks". If they are holding up a hiring process to hear back from you, it is fair to make it happen quickly. And when I have been in similar situations, everyone who was interested in me was willing to speed up the process to make decisions possible.