Lipoma removed, learnt is was a lymph node. How common is it to have this?

I am 29. Discovered a bump on my armpit 6 month ago. Ultrasound showed 2 lymph node inflammed and a large lipoma (2-4-5cm). After removal, the mass got biopsy, and I just learnt from the surgeon that it was not a lipoma, but a big lymph node. He went on explain to me that fat deposited inside the lymph. I do not know the medical term of this. How common is it to have this ? Learning that it is a lymph node scares me a little, given that I know friends that had lymphomas in the past.