In order to fully understand quarantine you need to read the USDA aphis Red Boo. This is an excerpt with the important information highlighted in bold.
I would suggest you read the complete file to understand what backyard flock registration means
http://www.aphis.usda.gov/animal_health/emergency_management/downloads/hpai_response_plan.pdf
Section 4.3.1
In many cases, poultry on Contact Premises (CP) may also be depopulated as soon as possible.
Section 4.3.4
If HPAI has not been or cannot be detected on a premises, but epidemiological
evidence indicates that the disease has spread beyond the initial premises, the
premises should be treated as presumptive positive premises and control measures
implemented.
Section 4.3.5
Personnel may also depopulate poultry on any CP meeting the criteria for a
presumptive case.
5.13 MASS DEPOPULATION AND EUTHANASIA
Poultry on an IP will be depopulated as soon as possible after declaration of an
HPAI outbreak.
Poultry on CP may also be depopulated as soon as possible after
the premises are classified as CP. The Mass Depopulation and Euthanasia SOP
provides instructions for personnel following the declaration of an HPAI outbreak
and the classification of IP and CP. This SOP offers HPAI-specific information
on mass depopulation and euthanasia for poultry, including evaluation of various
euthanasia methods, such as
In short there is nothing stopping them from depopulation of nearby areas if they presume said Contact Premises zone is also infected.