"Are you serious? The only difference between a vintage MTB and a road bike are tires and drop handle bars, of course you can use an MTB as a touring bike."
Not true, there are lots of differences, whether these are significant to you or not is another mater, particularly for shorter stature riders MTBs could be just the ticket, other than the weight of the tubes. Between the two, nothing is different, apart from everything. So if you look at every part, dimension and angle on the bikes it's probably different.
Also, not significant if people are buying an MTB for touring, but my vintage MTB is also different than my vintage style touring bike, because I bought it one size smaller, which was certainly the plan then. But obviously I could get a larger version.