A fellow in my evening class did his dissertation on composting. He was out at the plants that process the councils' green waste taking samples. He said these places sometimes (frequently) have compost fires in the windrows due to the intense heat generated by the microbiota. (the owner of the local one has coils circulating heat to his home and it's toasty all the year round).
The coal tar smell may be the result of partially-burned wood from one of these fires. If it is sooty that is also further evidence to suspect a compost fire has occurred.
In instances where a significant fire has occurred an EPA / SEPA investigation takes place and involves the Environmental Health, Public health departments, NHS and will be a matter of public record.
Most green waste collections are fortnightly. Waste has often generated significant heat by the time it is collected (I just probed my and my neighbour's 13 day old green waste and it is 21°C, significantly higher than ambient). The more biomass that is there the smaller external surface (heat dissipation) area to volume ratio. Depositing heated biomass onto already heated biomass just compounds the heat problem.
Some of the processors have a grading system. There is BSI PAS100 material they can sell to agriculture and professional horticulture. The rest can't be sold as a compost in its raw state but can be sold as a soil (structural) conditioner or further processed to make it sellable as compost. They are usually paid by the local authority to process the green waste, so it's dirt cheap per tonne if one can collect.
Talking of this I need to organise a field trip to the local green waste processors for the horti association. It's quite hi-tech and an interesting although organic-smelling day out, according to the green waste chap at the council.