Am very much the same, took a bunch private two years ago for multitude of reasons. I can, however, see why no public repos could be a partial indicator and of concern, in conjunction with sudden star growth, simply because it is hard for a person with no prior project to suddenly and publicly strike gold. Even on Youtube it is a rare treat to stumble across a well made video by a small channel and without algos to surface repos on Github in the same way, any viral success from a previously inactive account should be treated with some suspicion. Same the other way, if you never made any PR, etc. sudden engagement is a bit odd.