This is false. There are several developers working on knots. nostr:nprofile1qqszrqlfgavys8g0zf8mmy79dn92ghn723wwawx49py0nqjn7jtmjagpz4mhxue69uhhyetvv9ujuerpd46hxtnfduhszrnhwden5te0dehhxtnvdakz7qghwaehxw309aex2mrp0yhxummnw3ezucnpdejz7sujtmp proved this out a while back.
Discussion
It seems to have about 12 active developers who deliberately contribute to it
That is a lot different from having 1 such developer, but it's still not enough to be safe imo
It is also good that much of the code is the same as what's in Core, it means a lot of the review effort put into Core helps Knots too