At least to a 3rd party, it’s literally impossible to know why a colleague asks another to “slow down” without more context. I would however highly, highly recommend you 1) ask the colleague, softly, what they meant and 2) ask your manager about the situation.
For context, reasons I have asked colleagues to “slow down”:
- they were making many mistakes or suboptimal choices, sometimes really bad mistakes, and weren’t correcting when given feedback. Most of these cases, they seemed blissfully unaware of the work they were creating and the negative value they were adding.
- they were good engineers, but obviously burning out and miserable, which made it hard to give any criticism or suggest alternate approaches. See also “heroes”, the always-mega-swamped, and the perennially grumpy (these are different classes, but can be mixed). They also weren’t always aware of their effect on others.
- they were sidelining other peoples views and autonomy, demanding changes in other peoples components, making decisions outside their scope and domain of expertise, informally managing other folks work who were perfectly capable. This was usually done with a nice professional sheen — for example, “demanding changes” often takes the form of 1) writing full on features in another component, 2) making their own work kinda depend on that feature, 3) (finally) starting a very late convo with the maintainer of that component and putting them in a rough spot if the change was a bad idea from a broader perspective. Again, usually unaware.
It’s very easy to make the above mistakes — I have, most engineers probably have teetered, and I’ve seen it a bunch in my relatively short career.
I can say, I have never asked someone to slow down when they were hitting home runs, collaborating well, and making me look bad (please, I love to work with folks I can learn from, that’s engineering). It has always been a complex but totally salvageable performance problem I’m trying to guide back on track.