There's no accounting for fashion, I suppose. It's interesting to note that those puffy shorts (breeches) ultimately developed into trousers, while the trousers worn back in the ancient era ultimately developed into socks.

As for the wearing of tartan in the 16th century, there's no doubt it existed. For Highlanders a tartan mantle, worn over a knee-length leine, with bare legs below the knee, would be appropriate. James V, who was not a Highlander, was known to wear tartan hose/trews. (However, I'm not certain exactly when the word "tartan" came to be equivalent to the Gaelic breacan, so I suppose he could have just been wearing linsey-woolsey hose in a single color.) Also, an unknown man whose body was discovered in Ulster wore tartan hose, although he has been dated to the early 17th century rather than the 16th century.

Lastly, as for bonnets, it is my understanding that the 16th-century male Highlander would be bare-headed. At least, I am not aware of any headgear worn by them in this period. I think the 1631 woodcut of the Highland mercenaries serving Gustavus Adolphus is the earliest evidence of Highlanders wearing the bonnet.