I had seen the job offer a month before, with a trip in between, so the moment I sent my portfolio was quite blurry in my memory . I replied that I thought it was through InfoJobs, but it wasn't, they told me it had been through Domestika. I imagine that these kind of questions are to see if you are actively seeking employment or if you have more selection processes in progress. In my case I was looking for work for a while, so I opened every day all possible websites to look at new offers.