The latest update to Touchable app uses the regular USB-lightning cable to send and receive MIDI data (see here). How is this possible? Does this mean they are an MFi developer?
(I have read through the MFi FAQ but this case seems to not be covered)
Yes, they are a MFi certified company. To develop an accessory that uses either the official Apple 30-pin connector or Lightning connector you have to be a part of the MFi program.