Stutter or Language Development /Bilingual?

Stutter or Language Development /Bilingual? My child is 5 years old and recently started kindergarten. His English language skills have drastically grown over this time. Prior to kindergarten he primarily spoke our native language at home (and he only learned English a little over a year ago when he started half time PreK). I am not sure if this is a development language thing or a stutter. He only does it sometimes—when he is excited and telling a story or explaining a concept. It seems like his brain is moving faster than his mouth. And he does it for a few words here and there (like trips over the word 2 or 3 times or says um um or so so so). I’m trying to figure out if he needs to be evaluated or if this just something that will pass with time. It’s been a bit more pronounced over the last two months. My husband seems to think it is how most children his age speak (drawn out and tripping over words when excited or telling a story). No one has noticed except myself and his teacher also mentioned that she noticed an increase in this over the last two months, but it hasn’t affected him in the class. He also seems to do it much less in the native language, and I am constantly reminding him to speak the native language at home so I’m not if the switching back and forth is contributing. Have any parents had a similar experience with kids speaking like this around this age? Any bilingual children who have had this happen? Thank you so much for any experience or advice!