Scored a single. But you can clearly see in the video (about 1:40 mark) that his teammates mob him just before he reaches second.
https://video.search.yahoo.com/search/video?fr=mcafee&p=game+5+nlcs+1999+robin+ventura#id=1&vid=c190b8744659e4660311b01ddde0fa39&action=click
After Ventura touched and rounded first base, he incessantly waved over-enthusiastic teammates away so he could round the bases. But their exuberance was too much to allow their hero to savor a home-run trot. Instead, they mobbed Ventura before he reached second. “As long as I got to first base, I don’t care,” Ventura said. “It means we won.”4 Because of the human basepath blockade and because he never touched any of the remaining bases, the “Grand Slam Single” was forever cemented in franchise lore. But whether the final score read 4-3 instead of 7-3 was of little consequence to the joyous Mets. They had risen from the dead once more with another life to spare.