Looks like someone has drilled and tapped a hole into the water jacket in the inlet manifold. Maybe it was for another temperature sensor for an electric fan, temperature gauge or whatever? The bolt is now just plugging the hole.
I’m with Richard, possibly was going to fit an electric fan and drilled for temperature sensor.
easy enough to tidy it up, shorten the bolt and reinsert with thread lock, which hopefully will also seal it nicely, an Allen key bolt would be even neater.