tomato disease in Honey drop plants

Hi, Has anyone grown Honey  Drop tomato before. This is the first year I have tried them. The seedlings looked great and were doing very well. I potted them up to larger pots 2 weeks ago and then a few days later all the plants looked like they had a fungus /disease, while none of the other tomato plants did. All were grown in the same soil and in the same area. I tossed the lot in the trash as I didn't want anything to spread. I just checked the remainging plants and all looked good. So was it just the honey drops or was it something on the seeds ? I have some seeds left and will try again next year. But was just wondering if any one else has run into this?

This is also my first year growing Honeydrop My Honeydrop seeds came from Quail Seeds.  My seedlings are doing well but I have not potted them up yet.   They do however look a bit purplish which I have put down to getting cold.  I will move them to a warmer area when I pot them on.

I am south of boston, and  the plants were inside and warm. I got my seeds from SeedsN Such.