Tom arranged the meeting. We don't know exactly how, or who contacted who, but you will recall that after the horsehead scene Tom is telling Vito about the meeting and over the narrative we see Sollozzo climbing the stairs inside Genco.
As consigliere Tom had to have as much background on Sollozzo as possible. Remember Vito's lesson, keep your friends close, but your enemies closer. Sollozzo was acknowledging Tom's background check and acknowledging that it was true. He was looking for Vito's support, so hiding things in the meeting would not help to create the alliance Sollozzo was looking for. But as we know Vito nixed the plan.