Welcome to the forum.
A swollen toe may be caused by a number of things, but primarily it is either injury or infection. The blood doesn't really tell us much, since it can be caused directly by an injury which caused the swelling, or your guinea pig has become irritated at the soreness of the already swollen toe. In either case, since your pig is unaffected by the problem toe, I would not worry about it too much, but do monitor the toe closely and consider treating as follows.
Whether the swelling is the primary or secondary problem, treating the toe should be simple enough. Bathing in an antiseptic solution twice daily will help keep the toe clean - you can use saline/salt water, diluted Povidone Iodine, or diluted Savlon (active ingredient being Chlorhexidine Gluconate - be sure to check). I am unsure of the safety of TCP but I am aware how it could be beneficial; personally I would stick to saline for now just to be on the safe side.
If the toe remains swollen for another couple of days, it should be determined what kind of infection is present and further, specific treatment tried. The treatment is different for each infection - a bacterial infection can be treated with either oral antibiotics or a topical antibiotic ointment. A bacterial infection is the most likely provided the pig does not have a history of skin problems.
The other is a fungal infection, which can get into the nail bed and cause swelling in the toe - this needs treating with a topical antifungal cream, such as Daktarin cream (containing miconazole). A fungal infection in the toe will typically be the case if the pig has been known to have a fungal skin condition (which is often present on the feet).
