Rangers went ahead through Adel Taarabt's stunning 25-yard strike, but were pegged back by a penalty from Graham Alexander, the first league goal they have conceded at Loftus Road this season.
Williamson pointed to the spot after Matt Connolly sent Dean Marney sprawling in the area in first-half stoppage-time, but Warnock was not impressed with the decision.
"I didn't think it was a penalty at the time and I still don't after looking at it again," Warnock said.
"I don't now how he can give it from his position. He said to me my lad caught him with his foot but my lad was nowhere near him.
"I thought he had a really bad day at the office. It started in the first minute – we had a clear corner and he and the linesman gave a goal kick – and got worse from there."
Williamson's performance did not go unnoticed by Burnley boss Brian Laws either, after the official booked Chris Eagles for diving in the area following Clint Hill's challenge.
Former Sheffield Wednesday manager Laws said: "It was a scrappy game and the referee should take responsibility for that – was the game too big for him?
"I've had to make decisions because of him. I took Chris Eagles off because I thought he would send him off.
"Eagles is an honest lad, he's got a fat lip to show from it (Hill's challenge) and it wasn't from me!"
Tommy Smith and Shaun Derry could have won it for Rangers in stoppage time but the Clarets held out.
And Laws saluted his side's efforts after revealing a sickness bug had swept through the club earlier this week.
"I am delighted with the players. We had six players violently ill on Wednesday and they've gone out and given a tremendous performance," added Laws.
"I thought we were the better of the two teams. I was disappointed we didn't take all three points
"But we're the first team to score here this season which shows how hard it is."
Cardiff have now leapfrogged QPR at the summit, although it may be harsh to say Rangers' form is stuttering after they extending their club-record unbeaten start to the season to 14 games.
But four successive draws suggest the division will not be the cakewalk it appeared a month ago when the Hoops were steamrollering everyone in sight in the Championship.
Former Sheffield United manager Warnock admitted: "Frustration creeps in when you don't take your chances and at the moment we are not scoring enough goals.
"But it's now 14 games and we're nearly into November so I can't fault them."
QPR: Kenny, Walker, Connolly, Gorkss, Hill, Derry, Faurlin, Ephraim (Agyemang 62), Taarabt (Smith 82), Mackie, Hulse (Clarke 74). Unused substitutes: Cerny, Orr, Leigertwood, Rowlands.
Burnley: Grant, Mears, Carlisle, Duff, Fox, Eagles (Wallace 46), Alexander, Marney, Elliott, Rodriguez, Iwelumo (Thompson 83). Unused substitutes: Jensen, Cork, Paterson, Cort, Bikey.
Referee: I Williamson (Berkshire).
Man of the match: Graham Alexander.