Billy was an interested observer for Capital Radio at The Valley on Monday night and saw Jermain grab his second Premiership goal of the season with a superb volley.
"You just knew it was going to end up in the back of the even though it was not an easy one," he says.
"I was speaking to Jimmy Frith, who works with the kids, and he compared Jermain with Tony Cottee.
"He is a natural goalscorer and if he keeps progressing the way he is he will have a great career."
And he says he can understand why Charlton - the only other club Bonzo played for apart from West Ham - are disappointed that he left the club.
"The fee goes up to £1.6m if he plays so many games but he is worth that now - and he could be worth ten times that in five years time," insists Billy.
Of the game overall, he says: "I really enjoyed it; it was a terrific game, a throwback to the old days where you say 'go on lads, enjoy it, don't worry about defending but just try and score more goals than the other team.'
"The managers must have been pulling their hair out, though, because some of the goals were absolutely horrendous and the defending was non-existent.
"I have got fond memories of both clubs, of lot of affection for them; but their defending has to improve if they want results in the future."
And, as for Paul Kitson's performance, he says: "For me he has not really made it at West Ham and, having been out for a long time, the one thing you tend to do in reserve football is lose that sharpness around the box.
"But he was sharp as a razor on Monday night, and you have got to keep the man who has scored three for Saturday.
"If he had got another chance I think he'd have taken that as wellbut Defoe came on and scored what looked like the winning goal.
"The substitutions worked for Glenn, with him bringing Joe and Steve on as well; he had to change it when they were 3-2 down and looked like losing their way.
"Overall it was a cracking game and the fans must have gone away entertained."