Is pad thai actually Thai?
It's Thai, but it's a relatively new dish as it doesn't date back when the country was called Siam, and it uses Chinese style noodles and preparation (with Thai flavors).

There was a coup against the monarchy in 1932; in 1938 Plaek Phibunsongkhram (aka Phibun) came to power as prime minister.  Phibun ordered the creation of a new national dish, "Gway Teow Pad Thai" (Thai fried rice noodles).  The thing was, noodles weren't popular in Thailand before that, but there are stories that as this coincided with World War II, it was a way to get people to eat less rice.  (although, it's rice noodles, so I don't understand that part)

The government pushed for the dish, including subsidizing food carts (and banning non-Thai food cart vendors, so there wasn't competition from the Chinese noodle vendors)

...

But they're not the only country where foods we associate with them are relatively new -- potatoes and tomatoes are "new world" crops, not European, and untrusted (as they're part of the nightshade family along with capsicums (peppers), eggplant, and tomatillos).  So Irish and Italian cuisines before 1500CE (aka 1500AD) were extremely different from what we think of as their cuisines today.