Butter itself contains natural trans fat, so whipped butter would have it also. Small amount of natural-occurring trans fat shouldn't be a concern.
@Vickie has already given what I believe to be the correct answer, but I thought I'd add some more details.
The main trans fatty acid that occurs in butter, milk, yoghurt, etc is vaccenic acid. Another trans fatty acid called elaidic acid is also found in dairy products but in less quantity. These trans fatty acids are produced by bacteria in the guts of cows ("microbial hydrogenation") as a byproduct of metabolising non-trans fatty acids. Trans fatty acids are also found naturally in beef and lamb fat.
Some reading:Do trans fatty acids from industrially produced sources and from natural sources have the same effect on cardiovascular disease risk factors in healthy subjects? Results of the trans Fatty Acids Collaboration (TRANSFACT) study?
Full article at https://academic.oup.com/ajcn/article/87/3/558/4754416