A goal in time added on by substitute Lewis McGugan rescued a deserved point for Forest after Jay Bothroyd had given City a 63rd-minute lead.
Victory for the Bluebirds would have taken them to the top of the Championship but Jones was left frustrated by the outcome.
"We sat too deep and were punished for it," said the Bluebirds boss.
"It was a hard-earned point against a very good side who have good shape and can catch you on a counter-attack.
"We have four new players at the back and they are learning how to play at this level but we still have a long way to go in terms of being stronger as a unit."
In the wet and slippery conditions, Forest were the better side in the first half and all Cardiff had to offer was a Peter Whittingham volley that was turned over the bar by visitors' keeper Lee Camp.
The Forest midfield were on top with Paul Anderson causing problems down the left flank, and they should have had a penalty when he fell in the area following a challenge from Adam Matthews but the referee waved play on.
A halftime pep talk from Jones brought his side out in more determined fashion in the second period but even after going ahead they looked vulnerable at the back and the visitors fully deserved their late equaliser.
"I was both disappointed and concerned at half-time that we weren't two goals ahead and we also had a stonewall penalty turned down," said Forest manager Billy Davies.
"One lapse of concentration and we were a goal down but we came back strongly and it's a wonderful result.
"We have a lot of players out injured but we still put in a good performance and if we can maintain that standard then we should at least finish the season in mid-table."
Sporting Life