Tomatoes with an exserted (protruding) stigma are more susceptible to crossing. I never examined "Federle" closely, but my assumption would be that it has a stigma that protrudes from the stamens. Some heirlooms, especially potato-leaf types & currant tomatoes, often have protruding stigmas. Many modern tomatoes have an inserted stigma (completely enclosed by stamens) and are more likely to self-pollinate than to accept pollen from outside the flower.
ANY tomato
can cross, if the saved seeds are from a fused or imperfect flower, and/or if there is heavy pollinator activity. For seed saving, only perfectly-shaped tomatoes, with no blossom-end deformity & formed from single flowers, should be used. The first fruits, formed when pollinator populations are low, are also less likely to be crossed.
In my experience, paste tomatoes are less likely to cross... which is the reason I was so surprised by the heavy degree of crossing I observed in "Federle". In my saved seed, some were red (normal), some were pink, and some were orange. Apparently they had been... amorous... with every other tomato in the garden.

Oddly all of the crosses were normally shaped (or very close to it) regardless of color.
All that aside, "Federle" is a great tomato, and might not cross in your area
@heirloomgal ... but caveat emptor. You might want to give it extra space from other tomatoes, and shield it as much as possible. I have to do that when growing potato-leaf tomatoes for seed.