It is, that they are completely different strings.
Guitars have only six strings, so only six different thicknesses.
Many harps are strung with gut strings, and your typical concert harp will most likely have a combination of wire wrapped strings in the base, then gut strings, and then many use nylon in the upper octaves.
Guitars typically are strung completely in one or the other, metal or nylon.
Harp strings are color coded so you know which string is which note, Cs are red and Fs are blue, purple or black (most use blue).
The gauges of guitar strings are designed for guitars. The gauges for harp strings are designed for the harps, and different harps can have very specific requirements for gauges.
On guitars you can get away with swapping out to a different gauge string without much difficulty. On
Did you want to replace a broken harp string with the same gauge of nylon? I asked the same question about my Melody 26 and the reply came back “direct from Dwight, if you don’t want to wait, yes, any nylon .028 string will work “
Of course, if the original was color-coded for C or F you’ll have to figure out how to mark your makeshift replacement.