I believe he would be classed as a visa national basically meaning he will need a visa-I am not sure if he will need just a transit visa or a visit visa going through uk he will be subject to border control at london which is the UK main airport
In addition to needing a visa to enter the United Kingdom, nationals of Jamaica also need a visa to transit through the UK, known as Direct Airside Transit Visa (DATV).
All I can tell you is from experience is that trying to bring someone to the UK can be hard not only hard but takes effort time and money.UK rules about visas and I note in particular Jamaican visas but do not know the reason why are becoming harder to obtain -Much harder than ever before.People who try to bring their own blood relatives or children to the UK even for a holiday are having an extremely hard time of doing so right now.The situation I know of the person has a very good stable job here in the UK and they owned their own property plus money in the bank.Eventually 1 person out of the 2 applied for got through.
It was not a quick simple easy thing but I do not know exactly what you have to go through on Jamaica side.
I hear now not only do you have to proove you can keep the person but they have to proove that they have something worthwhile back in Jamaica that officials would think they would not want to leave forever.I also hear you have to now put up a bond of £1000 or something similar to that amount and you lose it if the person absconds.
This is just getting them to the UK,I have no idea how easy or hard it would be to then get them to malta you will have to check again on Maltas rules on Jamaican citizens travelling there.
Seems like your friend found a nice friend in you!own job house nice holiday place!Anytime you want a lodger let me know