The impressive victory at Ibrox means the Light Blues have now secured a record-breaking 19 consecutive wins.
But, despite maintaining their 100 per cent Scottish League One run so far this term, McCoist does not believe Rangers will win every league game this season.
Reflecting on the winning streak, he said: "It's a fantastic achievement for the players.
"They can be very proud of that run at the moment but it has to continue on Saturday against Ayr United.
"People will look at the opposition and say this, that and the next thing but, as we have seen this year in the cup competitions, the teams in the lower leagues are more than capable of winning games against teams with supposedly better squads.
"It's a great achievement and the boys will get the credit they deserve from ourselves and that's all that matters really."
Asked if Rangers will win every league game this season, McCoist added: "I genuinely don't think so. I really don't think that will happen.
"Anybody who has been to our away games at Forfar and Brechin this year will know how difficult it is and that's why I just don't think it will happen.
"I will settle for winning the league, that's what I will settle for.
"I'll stay well away from any predictions that would just stir up the opposition and, without doubt, come back and bite me on the backside."
Nicky Clark helped himself to four goals, with Lee Wallace and skipper Lee McCulloch also on the scoresheet after Gavin Swankie had levelled for Forfar.
Clark - who netted more than 40 goals in the same division with Queen of the South last season - now has seven goals this term after a relatively slow start for the Light Blues.
McCoist said: "Nicky has battered a few goals in, which will be great for him, against a team who have provided us with difficult games so far this season.
"He is a smashing lad who works really hard at his game.
"I think a lot of people, wrongly in my opinion, automatically thought he would just come in [and score goals] because he scored 40 goals last year with Queen of the South.
"But I've said it before, and I'm not sure everybody believes me, it's not just as easy to score here as a lot of people think.
"He continues to work hard and, when you do that, you've always got a chance of getting your rewards. This was a great day for him."
Forfar are the only team to beat Rangers this season, dumping them out of the League Cup in August.
And, despite McCoist's claims, boss Dick Campbell believes the Glasgow giants can win every league game.
He said: "They can now. I would think Alistair was more worried about us, than I was of them.
"I mean that. We'd played them twice and, both times, we could have won the game.
"It wasn't a fluke, albeit Alistair had a few players missing because of the embargo.
"I think they could [keep a 100 per cent record] after what I've seen tonight. It's got to be a good team to beat them at their level.
"Part-time clubs will struggle against them because they've got better players and they will win games.
"They are top of the league and they'll have it won by Christmas. They can put a reserve team out in the second half of the season and no-one will be near them."
- Sports & Recreation