You can invite users individually by tapping the little plus in the bottom right of the picture, by inviting your favorites, or by selecting "Invite all suggestions".

"Invite all suggestions" means that some members will be invited randomly. You can tap this button multiple times - invitations from you will never go out twice. The members that are suggested to you are all located near the meeting. The selection is therefore based on the location of the meeting. So it can not happen that members are invited who live hundreds of kilometers away.