Django queryset understanding confirmation

queryset_filters.py

#$ cat myapp/models.py 
#from django.db import models
#
#class Foo(models.Model):
#    pass
#
#class Bar(models.Model):
#    foos = models.ManyToManyField(Foo, related_name="bars")
#    val_a = models.BooleanField()
#    val_b = models.BooleanField()

# Ensure we're working on an empty set
Foo.objects.all().delete()
Bar.objects.all().delete()

# Create two Foo objects
fooA = Foo()
fooA.save()
fooB = Foo()
fooB.save()

# Create Bar objects with alternating values
bar_01 = Bar(val_a=False, val_b=True)
bar_01.save()
bar_10 = Bar(val_a=True, val_b=False)
bar_10.save()
bar_11 = Bar(val_a=True, val_b=True)
bar_11.save()

# Join to foos and the bars
fooA.bars.add(bar_01)
fooA.bars.add(bar_10)
fooB.bars.add(bar_11)

# Ensure sane joined filter results
queryset = Foo.objects.filter(bars__val_a=True, bars__val_b=True)
assert fooA not in queryset
assert fooB in queryset

# Ensure sane separate filter results
queryset = Foo.objects.filter(bars__val_a=True).filter(bars__val_b=True)
assert fooA in queryset
assert fooB in queryset